Containers of cooled beverages form surfaces on which airborne moisture condenses. The condensate drips down the sides of the container (such as a glass containing an iced beverage) and onto the surface that is supporting the container. Where that surface is wood, damage can result. Where that surface is glass, plastic or metal, the condensate will collect, pool and spread, oftentimes wetting nearby items such as paper napkins, making the supporting surface slippery, and in general creating a mess.
To meet this problem, coasters have long been known in the art. A coaster typically is flat (although in some designs, there is an appreciable sidewall) and can be constructed of stone, rubber, glass, wood, plastic, metal or cardboard, or composites of these. Many coasters are round and sized to fit the bottom of a glass or drink container; others have been provided that are polyhedral or irregular in outline. It is further known to create a reservoir in the coaster for condensate, by constructing ribs or bumps to stand up from a coaster floor, such that the bottom of the beverage container is supported above the coaster floor. It is also known to support a coaster main body off of a supporting surface (such as a table) by legs or bumps, so as to create an air gap underneath the coaster and increase its insulative effect.
A coaster may also be used to protect the supporting surface from the bottom of a sharp or abrasive object. Some coasters have been proposed that have the effect of increasing the coefficient of friction between the item supported and the supporting surface; these typically are molded of an elastomer and have upstanding and/or depending features with sharp edges.
While it is known to mold or affix bumps or ribs into or onto the upper and/or lower surface of the main coaster body, doing so creates corners, crevasses or channels in which (wet) dirt or other contaminants may accumulate and which are difficult to clean. A need therefore persists for a friction-enhancing coaster that presents a moisture-impermeable barrier, is furnished with a condensate reservoir, and creates an insulative air gap, but nonetheless is easy to keep clean.